Liquid-immersed transformer temperature rise calculation method

Abstract

This invention provides a method for calculating the temperature rise of a liquid-immersed transformer. The method includes: Step S1: Establishing a thermal circuit calculation model for the average oil temperature of the transformer and a coupled calculation model of electromagnetic and fluid properties; Step S2: Obtaining the thermal resistance R and total heat capacity ∑C of the transformer. SUM And the heat source, to obtain the average oil temperature θ of the transformer. om Then, the oil temperature θ at the transformer's radiator outlet is obtained. bo θ is the oil temperature at the radiator outlet. bo The open boundary inflow temperature is used in the coupled calculation model; Step S3: Obtain the temperature distribution on the transformer to derive the temperature value T2 on the transformer's coil grid unit based on the temperature distribution; Step S4: Determine whether to correct the conductivity; Step S5: After correcting the conductivity, repeat steps S2, S3, and S4 until the temperature distribution converges. This invention solves the problems of low calculation efficiency and poor accuracy in existing liquid-immersed transformer temperature rise calculation methods.

Description

Technical Field

[0001] This invention relates to the field of high-voltage power transmission and distribution technology, and more specifically, to a method for calculating the temperature rise of a liquid-immersed transformer. Background Technology

[0002] Currently, liquid-immersed transformers are the most important equipment in high-voltage power transmission and distribution systems. With the increasing investment in ultra-high-voltage long-distance power transmission and the rapid increase in the capacity of individual liquid-immersed transformers, the resulting localized overheating caused by losses is becoming increasingly prominent, placing higher demands on the reliability of liquid-immersed transformers. Specifically, transformer temperature rise is the most important indicator, directly affecting the transformer's lifespan and the safety of the power system. As the temperature rises, the deterioration rate of the transformer's oil-paper insulation system accelerates significantly, easily leading to insulation failure. Furthermore, for every 6°C increase in the hot spot temperature within a liquid-immersed transformer above the design value, the transformer's service life is halved. Therefore, precise control of transformer temperature rise during the design process is crucial. At the same time, calculating the temperature rise of liquid-immersed transformers (especially the hot spot temperature rise) is also a challenging aspect of transformer design.

[0003] In existing technologies, engineering analytical methods, thermal circuit modeling methods, and numerical calculation methods are commonly used to obtain the temperature rise of transformers. However, all three of these temperature rise calculation methods have certain problems or limitations, making it difficult to achieve efficient and accurate transformer temperature rise calculations. Summary of the Invention

[0004] The main objective of this invention is to provide a method for calculating the temperature rise of a liquid-immersed transformer, thereby solving the problems of low calculation efficiency and poor accuracy in existing methods for calculating the temperature rise of liquid-immersed transformers.

[0005] To achieve the above objectives, this invention provides a method for calculating the temperature rise of a liquid-immersed transformer, comprising: Step S1: establishing a thermal circuit calculation model for the average oil temperature of the transformer and establishing a coupling calculation model between the electromagnetic and fluid currents of the transformer; Step S2: obtaining the thermal resistance of the transformer. Total heat capacity And the heat source, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. And based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. Then adjust the oil temperature at the radiator outlet. As the open boundary in the coupled calculation model, the incoming flow temperature; Step S3: Obtain the temperature distribution on the transformer, and derive the temperature value T2 on the transformer's coil grid unit based on the temperature distribution; Step S4: Based on the absolute value of the difference between the preset temperature value T1 and the temperature value T2, and the preset value... between the two to determine whether the conductivity needs to be corrected; step S5: after the conductivity is corrected, repeating step S2, step S3 and step S4 until the temperature distribution on the transformer presents a convergent state.

[0006] Further, the average oil temperature of the transformer is derived according to the thermal resistance , the total heat capacity and the heat source, which includes: deriving according to the equation: ; wherein, is the initial average oil temperature within a calculation duration, is the final average oil temperature within the calculation duration, is the core loss of the transformer, is the ohmic loss of the coil of the transformer, is the stray loss within the other metal structural parts of the transformer; is the heat dissipated to the air by the transformer; the core loss , the ohmic loss of the coil of the transformer and the stray loss within the other metal structural parts of the transformer are derived according to the electromagnetic parameters of the transformer through simulation calculation.

[0007] Further, the core loss , the ohmic loss of the coil of the transformer and the stray loss within the other metal structural parts of the transformer are derived according to the electromagnetic parameters of the transformer through simulation calculation, which includes: step S01: establishing a magnetic field simulation model according to the electromagnetic design parameters of the transformer; step S02: inputting material properties into the magnetic field simulation model; step S03: taking the current at the minimum voltage tapping as the excitation of the magnetic field simulation model.

[0008] Further, the total heat capacity is derived according to the equation: ; wherein, is the mass of the core and the coil, is the mass of the tank and the accessories, is the mass of the oil in the transformer; or, the total heat capacity is derived according to the equation: ; wherein, is the tank heat capacity correction factor, is the core heat capacity correction factor, is the coil heat capacity correction factor, is the oil heat capacity correction factor in the transformer, is the insulation material heat capacity correction factor, is the weight of the tank.for the oil tank specific heat capacity, for the core weight, for the core specific heat capacity, for the coil weight, for the coil specific heat capacity, for the transformer oil weight, for the transformer oil specific heat capacity, for the insulation material weight, for the insulation material specific heat capacity.

[0009] Further, the liquid-immersed transformer temperature rise calculation method further comprises: step S11: obtaining the oil tank weight , the core weight , the coil weight , the transformer oil weight , the insulation material weight of the transformer as input data, obtaining the heat capacity measured value of the transformer as output data; step S12: constructing a BP neural network and training the BP neural network multiple times to establish a total heat capacity model.

[0010] Further, the neuron net input and the neuron output of the BP neural network satisfy: ; ; wherein, is each input data, is a heat capacity correction factor, is a threshold value.

[0011] Further, the liquid-immersed transformer temperature rise calculation method further comprises a step S110 between step S11 and step S12: normalizing the oil tank weight , the core weight , the coil weight , the transformer oil weight , the insulation material weight obtained by step S11 and the heat capacity measured value of the transformer.

[0012] Further, the method for obtaining the thermal resistance of the transformer comprises: obtaining according to the equation: ; wherein, is a heat transfer coefficient and satisfies: , is a Nusselt number and satisfies: , is a convective heat transfer correlation coefficient, is a characteristic length, is a thermal conductivity, is a heat dissipation area, It is a Grashof number and satisfies: , It is a Prandtl number and satisfies: , For density, For dynamic viscosity, It is the acceleration due to gravity. The rate of change of volume, This refers to the temperature difference.

[0013] Furthermore, based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. The methods include: based on the equation: The conclusion is that, The temperature difference between the inlet and outlet of the transformer radiator must satisfy the following: , This is a correction function for the center height of the coil and the center height of the heat sink.

[0014] Furthermore, methods for obtaining the temperature distribution on a transformer include: using fluid-structure interaction (FSI) physical field calculations to determine the temperature distribution on the transformer.

[0015] Applying the technical solution of this invention, a thermal circuit calculation model for the average oil temperature of the transformer is first established, and a coupling calculation model of the electromagnetic and fluid properties of the transformer is established. Then, the thermal resistance of the transformer is obtained. Total heat capacity And the heat source, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. And based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. Then adjust the oil temperature at the radiator outlet. The temperature is used as the open boundary in the coupled calculation model. Next, the temperature distribution on the transformer is obtained, and the temperature value T2 on the transformer's coil grid cell is derived from this distribution. Then, the absolute value of the difference between the preset temperature value T1 and the temperature value T2 is compared with the preset value... The relationship between the two factors determines whether conductivity correction is needed. If conductivity correction is required, the oil temperature at the transformer's radiator outlet should be recalculated after correction. Then adjust the oil temperature at the radiator outlet. As the open boundary inflow temperature in the coupled calculation model, the temperature distribution on the transformer is re-acquired, and the temperature value T2 on the transformer's coil grid cell is obtained based on the temperature distribution. Then, the absolute value of the difference between the preset temperature value T1 and the temperature value T2 is compared with the preset value. The relationship between the temperature distribution and the conductivity is judged whether the conductivity needs to be corrected, and the process is repeated until the temperature distribution on the transformer presents a convergent state. In this way, the transformer temperature rise calculation method based on the thermal circuit method and the numerical calculation method realizes efficient and accurate calculation of the transformer temperature rise and accurate positioning of the hot spot temperature rise position, makes up for many problems in the traditional liquid-immersed transformer temperature rise calculation, and further solves the problems of low calculation efficiency and poor accuracy of the transformer temperature rise calculation method in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings constituting a part of this specification illustrate further aspects of the present application, and together with the description and drawings, serve to explain principles of the present application. In the drawings:

[0017] Figure 1 A flow chart of an embodiment of the liquid-immersed transformer temperature rise calculation method according to the present application is shown;

[0018] Figure 2 A thermal circuit calculation model diagram of the transformer average oil temperature of the liquid-immersed transformer temperature rise calculation method in Figure 1

[0019] Figure 3 A BP neural network model diagram of the liquid-immersed transformer temperature rise calculation method in Figure 1

[0020] Figure 4 A BP neural network analysis flow chart of the liquid-immersed transformer temperature rise calculation method in Figure 1

[0021] Figure 5 A temperature distribution nephogram calculated by the liquid-immersed transformer temperature rise calculation method in Figure 1

[0022] A temperature distribution nephogram calculated by the traditional numerical calculation method is shown; Figure 6

[0023] A temperature rise experimental result comparison diagram is shown. Figure 7 DETAILED DESCRIPTION

[0024] It should be noted that the embodiments and features in the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0025] It should be noted that, unless otherwise specified, all technical and scientific terms used in the present application have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0026] ​​​​In this invention, unless otherwise stated, directional terms such as "up" and "down" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction; similarly, for ease of understanding and description, "left" and "right" are generally used in relation to the left and right shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0027] To address the issues of low computational efficiency and poor accuracy in existing methods for calculating the temperature rise of liquid-immersed transformers, this application provides a method for calculating the temperature rise of liquid-immersed transformers.

[0028] like Figure 1 As shown, the method for calculating the temperature rise of a liquid-immersed transformer includes:

[0029] Step S1: Establish a thermal circuit calculation model for the average oil temperature of the transformer and establish a coupling calculation model for the electromagnetic and fluid properties of the transformer;

[0030] Step S2: Obtain the thermal resistance of the transformer Total heat capacity And the heat source, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. And based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. Then adjust the oil temperature at the radiator outlet. Temperature is introduced as an open boundary in the coupled computational model;

[0031] Step S3: Obtain the temperature distribution on the transformer, and derive the temperature value T2 on the transformer's coil grid unit based on the temperature distribution;

[0032] Step S4: Based on the absolute value of the difference between the preset temperature value T1 and the temperature value T2, and the preset value... The relationship between the two factors determines whether conductivity needs to be corrected.

[0033] Step S5: After correcting the conductivity, repeat steps S2, S3 and S4 until the temperature distribution on the transformer converges.

[0034] Applying the technical solution of this embodiment, a thermal circuit calculation model for the average oil temperature of the transformer is first established, and a coupling calculation model of the electromagnetic and fluid properties of the transformer is established. Then, the thermal resistance of the transformer is obtained. Total heat capacity And the heat source, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. and the average oil temperature of the transformer is obtained according to the transformer average oil temperature the oil temperature at the radiator oil outlet of the transformer is obtained the oil temperature at the radiator oil outlet of the transformer is obtained again the temperature at the open boundary of the coupling calculation model is taken as the flow temperature. Then, the temperature distribution on the transformer is obtained, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution. Then, whether the conductivity needs to be corrected is judged according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value If the conductivity needs to be corrected, the oil temperature at the radiator oil outlet of the transformer is calculated again after the conductivity is corrected the oil temperature at the radiator oil outlet of the transformer is obtained again the temperature at the open boundary of the coupling calculation model is taken as the flow temperature. Then, the temperature distribution on the transformer is obtained, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution. Then, whether the conductivity needs to be corrected is judged according to the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value , and the process is repeated until the temperature distribution on the transformer converges. In this way, the transformer temperature rise calculation method based on the thermal circuit method and the numerical calculation method realizes efficient and accurate calculation of the transformer temperature rise and accurate positioning of the hot spot temperature rise position, and solves the problems of low calculation efficiency and poor accuracy of the existing liquid-immersed transformer temperature rise calculation method.

[0035] In the embodiment, the electromagnetic and fluid coupling calculation model of the transformer is established by determining the electromagnetic design parameters and the structural design parameters of the transformer (including the main structural parameters of the transformer, the materials used by the main components, and the size and number of the external fin heat sinks, etc.).

[0036] As shown in Figure 2 , according to the oil circulation process in the transformer and the principle of energy balance, a thermal circuit calculation model of the average oil temperature of the transformer is established.

[0037] In the embodiment, from the analysis of the physical process of the transformer heat dissipation, when the oil flow temperature and speed reach stability, the temperature of the core and the coil and other components no longer continues to rise, and the excess heat is completely transferred to the external environment through heat circulation. At this time, the heat generation and cooling of the transformer reach balance. At this time, the hot spot temperature in the transformer usually appears at the upper position of the coil, and the hot spot temperature is one of the most critical factors limiting the load capacity of the transformer and evaluating the service life of the transformer.

[0038] In the embodiment, the dynamic thermal circuit model is used to calculate the average oil temperature of the transformer, and the oil temperature at the radiator oil outlet entering the coil of the transformer is calculated according to the average oil temperature ​ The obtained oil temperature at the radiator outlet By using the incoming flow temperature as an open boundary, the traditional closed self-circulating transformer fluid-structure interaction calculation model is simplified into a fluid-structure interaction calculation model with an open boundary inside the transformer body. This greatly simplifies the solution process and shortens the calculation time while ensuring the accuracy of the calculation.

[0039] In this embodiment, the variable step size method is used to calculate the average oil temperature of the transformer. Therefore, since the specific heat capacity, thermal conductivity, viscosity, and density of insulating oil are all quantities that change with temperature, it is necessary to use dynamic equations to calculate the average oil temperature at steady state.

[0040] In this embodiment, the temperature distribution is calculated using the physical field of fluid-structure interaction, and the conductivity is corrected. The temperature rise distribution within the coil is then recalculated, and this process is repeated until the temperature rise value meets the convergence requirement, at which point the calculation is complete. Specifically, a thermal circuit calculation model for the average oil temperature of the transformer is first established. A method for calculating the total heat capacity within the transformer with correction factors is proposed. Combining experimental data from previous transformers (especially for transformers with special insulating media, such as natural ester insulating oil transformers), a BP neural network is used to obtain heat capacity correction factors with different characteristic parameters, thereby improving the accuracy of the total heat capacity calculation and making this average oil temperature thermal circuit model applicable to special liquid-insulated transformers. Thus, based on the calculation method of the transformer's self-circulating physical process and characteristic temperature, a combination of the thermal circuit method and numerical calculation method is proposed, simplifying the traditional transformer self-circulating calculation model. That is, the self-circulating calculation model is simplified into a calculation model with open boundaries, which greatly improves engineering efficiency while ensuring calculation accuracy.

[0041] In this embodiment, a numerical calculation model of the fluid within the transformer body is established. The calculation model only includes the transformer body, namely the low-voltage coil, high-voltage coil, voltage regulating coil, and corresponding insulation structures. The insulation structures include paper tubes, electrostatic plates, pressure plates, and oil guide plates within the coils. The boundary condition is an open boundary, which can automatically allocate the flow rate in and out of the boundary. The incoming flow temperature entering this calculation domain is the oil temperature at the radiator outlet. .

[0042] In this embodiment, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. The methods include:

[0043] According to the equation: The conclusion is as follows. Among them, The initial average oil temperature over a calculation period. The final average oil temperature over a calculation period. For transformer core losses, is the ohmic loss of the coil of the transformer, is the stray loss in other metal structural parts of the transformer; is the heat dissipated by the transformer to the air; the core loss of the transformer is calculated by simulation according to electromagnetic parameters of the transformer , the ohmic loss of the coil of the transformer and the stray loss in other metal structural parts of the transformer .

[0044] In the embodiment, the method for calculating the core loss of the transformer , the ohmic loss of the coil of the transformer and the stray loss in other metal structural parts of the transformer according to electromagnetic parameters of the transformer includes:

[0045] Step S01: establishing a magnetic field simulation model according to electromagnetic design parameters of the transformer;

[0046] Step S02: inputting material properties into the magnetic field simulation model;

[0047] Step S03: taking the current at the voltage minimum tapping as the excitation of the magnetic field simulation model.

[0048] Specifically, taking a natural ester insulating oil transformer as an embodiment, the model number is SWZ-100000 / 220, the transformer includes a transformer oil conservator, a manifold, a radiator, a high-voltage bushing, a neutral point bushing and a transformer oil tank, and the basic performance parameters are shown in Table 1. In step S01, the magnetic field simulation model is established according to finite elements. In step S02, the material properties include the materials of the coil, the core and other metal structural parts, and the specific material property setting conditions are shown in Table 2. At the same time, the transformer in the embodiment is a load regulation transformer, and the heat source in the temperature rise test is the loss generated at the voltage minimum tapping (at this time, the current is maximum, and the loss of the transformer in operation is also maximum), so the input excitation is the current at the voltage minimum tapping, at this time, there is a loss density distribution in the low-voltage coil, the high-voltage coil and the voltage regulation coil.

[0049] Table 1 Basic performance parameters of SWZ-100000 / 220 transformer

[0050]

[0051] Table 2 Material properties for magnetic field calculation of SWZ-100000 / 220 transformer

[0052]

[0053] Wherein, the coil material is electrical copper, the core material is silicon steel sheet and its permeability follows B-H curve, the material of other metal structural parts is A3 steel and its permeability also follows B-H curve.

[0054] Optionally, the method for obtaining the total heat capacity comprises:

[0055] According to the equation: , wherein, is the mass of the core and the coil, is the mass of the oil tank and accessories, is the mass of the oil in the transformer; or, according to the equation: , wherein, is the oil tank heat capacity correction factor, is the core heat capacity correction factor, is the coil heat capacity correction factor, is the oil in the transformer heat capacity correction factor, is the insulation material heat capacity correction factor, is the oil tank weight, is the specific heat capacity of the oil tank, is the core weight, is the specific heat capacity of the core, is the coil weight, is the specific heat capacity of the coil, is the oil in the transformer weight, is the specific heat capacity of the oil in the transformer, is the insulation material weight, is the specific heat capacity of the insulation material. In this way, the above arrangement makes the calculation of the total heat capacity more diverse to meet different use requirements and working conditions.

[0056] In this embodiment, the total heat capacity is obtained according to the equation:

[0057] .

[0058] In this embodiment, the liquid-immersed transformer temperature rise calculation method further comprises:

[0059] Step S11: obtaining the oil tank weight , core weight , coil weight , oil in the transformer weight , insulation material weight of the transformer as input data, obtaining the heat capacity measured value of the transformer as output data;

[0060] Step S12: Construct a BP neural network and train the BP neural network multiple times to establish a total heat capacity model.

[0061] Specifically, based on the weight of the transformer's oil tank Iron core weight Coil weight The weight of the oil inside the transformer Weight of insulation material As input to the network, the measured value of the transformer's heat capacity is used as the network output. Based on the historical experimental data of these characteristic parameters, the implicit relationship between these parameters and the total heat capacity of the transformer is learned through sample learning, and a transformer-specific total heat capacity model is established.

[0062] In this embodiment, the net input of neurons in the BP neural network and neuron output satisfy:

[0063] ;

[0064] .in, For each input data, This is the heat capacity correction factor. The threshold value is used.

[0065] like Figure 3 As shown, in the neural network model, for any neuron, , … The input to the neuron is often an independent variable that has a key impact on the system model (i.e., the weight of the fuel tank). Iron core weight Coil weight The weight of the oil inside the transformer Weight of insulation material ), , … The weighting of each input variable is adjusted to determine the connection weights. There are multiple ways to combine signals into the neuron; the most convenient method, linear weighted summation, yields the net input to the neuron. Among them, only when the information received by the neuron reaches the threshold... It will only be activated then, therefore and The comparisons are then processed through an activation function to produce the neuron's output. .

[0066] In this embodiment, the transfer function used in the BP neural network is the nonlinear transformation function Sigmoid function, which is characterized by the continuity of the function itself and its derivative. The equation of the activation function is:

[0067] (Equation 1)

[0068] In this embodiment, the process of solving the correction factor for transformer heat capacity using a BP neural network is as follows: Figure 4 As shown, the weight of each input variable solved by the algorithm is the heat capacity correction factor for each term, which is obtained through the equation. The corrected heat capacity of the transformer can then be determined. In this embodiment, the transformer is a natural ester insulating oil transformer.

[0069] In this embodiment, the method for calculating the temperature rise of a liquid-immersed transformer further includes step S110, which is located between steps S11 and S12: calculating the tank weight obtained in step S11. Iron core weight Coil weight The weight of the oil inside the transformer Weight of insulation material The measured values ​​of the transformer's heat capacity were normalized.

[0070] In this embodiment, the thermal resistance of the transformer is obtained. The methods include:

[0071] According to the equation: The conclusion is as follows. Among them, The heat transfer coefficient is and satisfies: , It is a Nusselt number and satisfies: , For convective heat transfer correlation coefficient, For characteristic length, Thermal conductivity, For heat dissipation area, It is a Grashof number and satisfies: , It is a Prandtl number and satisfies: , For density, For dynamic viscosity, It is the acceleration due to gravity. The rate of change of volume, This refers to the temperature difference.

[0072] Specifically, the equation for calculating the heat transfer coefficient h is as follows:

[0073] (Equation 2)

[0074] In the embodiment, the average oil temperature of the transformer is obtained according to the transformer average oil temperature The method for obtaining the oil temperature at the radiator outlet of the transformer includes the following steps.

[0075] The average oil temperature of the transformer is obtained according to the equation: wherein, the temperature difference between the inlet and outlet of the radiator of the transformer satisfies: and the correction function of the coil center height and the radiator center height is .

[0076] Specifically, since the specific heat capacity, thermal conductivity, viscosity and density of the insulating oil are all quantities that change with temperature, a dynamic equation is needed to calculate the temperature when the average oil temperature reaches a steady state. In order to realize dynamic average oil temperature calculation, a differential equation is used to establish the mathematical model, a variable step method is used to calculate the average oil temperature of the transformer, and the average oil temperature of the transformer at the steady state is calculated .

[0077] In the embodiment, the liquid-immersed transformer temperature rise calculation method further includes a step S04 located after the step S03:

[0078] The calculation results of the electromagnetic module are coupled to the fluid calculation module, and the relevant material parameters are input.

[0079] Specifically, the material properties of solid materials such as density, thermal conductivity and specific heat capacity are listed in Table 3, and the material properties of fluid materials such as viscosity, density, thermal conductivity and specific heat capacity are listed in Table 4.

[0080] Table 3: Solid material properties

[0081]

[0082] Table 4: Fluid material properties

[0083]

[0084] In the embodiment, the method for obtaining the temperature distribution on the transformer includes: using fluid-structure coupling to calculate the temperature distribution on the transformer.

[0085] Specifically, the fluid-temperature field calculation uses a convection heat dissipation calculation model and a heat conduction model. The overall temperature inside the transformer is low, and the influence of thermal radiation on heat dissipation can be ignored. After multiple conductivity corrections, the temperature rise inside the transformer body converges. The temperature distribution cloud diagrams obtained by the liquid-immersed transformer temperature rise calculation method of the embodiment and the traditional numerical calculation method are as follows: Figure 5 and Figure 6 ​​​As shown, the temperature distribution is basically the same. The hot spot temperature obtained by the liquid-immersed transformer temperature rise calculation method in this embodiment is 123℃, that is, a temperature rise of 103K. The hot spot temperature obtained by the traditional method is 124℃, that is, a temperature rise of 104K.

[0086] Experimental verification: The results obtained from the temperature rise experiment are as follows Figure 7 As shown, all results are converted into temperature rise, and the comparison of temperature rise calculation results is shown in Table 5.

[0087] Table 5 Comparison of Temperature Rise Calculation Results

[0088]

[0089] Specifically, Table 6 compares the calculation time of the liquid-immersed transformer temperature rise calculation method in this embodiment with that of the traditional two-dimensional axisymmetric calculation method.

[0090] Table 6 Comparison of Calculation Time

[0091]

[0092] In this embodiment, the calculation result of the liquid-immersed transformer temperature rise calculation method has a small error with the measured value, extremely high accuracy, and significantly shortens the calculation time, thus improving engineering efficiency.

[0093] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0094] First, a thermal circuit calculation model for the average oil temperature of the transformer is established, and a coupling calculation model of the electromagnetic and fluid properties of the transformer is established. Then, the thermal resistance of the transformer is obtained. Total heat capacity And the heat source, based on thermal resistance Total heat capacity And the average oil temperature of the transformer is obtained from the heat source. And based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. Then adjust the oil temperature at the radiator outlet. The temperature is used as the open boundary in the coupled calculation model. Next, the temperature distribution on the transformer is obtained, and the temperature value T2 on the transformer's coil grid cell is derived from this distribution. Then, the absolute value of the difference between the preset temperature value T1 and the temperature value T2 is compared with the preset value... The relationship between the two factors determines whether conductivity correction is needed. If conductivity correction is required, the oil temperature at the transformer's radiator outlet should be recalculated after correction. Then adjust the oil temperature at the radiator outlet. As the open boundary in the coupling calculation model, the temperature distribution on the transformer is reacquired, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution, and the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value is determined to determine whether the conductivity needs to be corrected The temperature distribution on the transformer is reacquired, and the temperature value T2 on the coil grid unit of the transformer is obtained according to the temperature distribution, and the relationship between the absolute value of the difference between the preset temperature value T1 and the temperature value T2 and the preset value is determined to determine whether the conductivity needs to be corrected

[0095] Obviously, the above-described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor should belong to the scope of protection of the present application.

[0096] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should be understood that when the terms "comprise" and / or "include" are used in the specification, there is a feature, step, work, device, component and / or combination thereof.

[0097] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-described drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein.

[0098] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for calculating the temperature rise of a liquid-immersed transformer, characterized in that, include: Step S1: Establish a thermal circuit calculation model for the average oil temperature of the transformer and establish a coupling calculation model for the electromagnetic and fluid properties of the transformer; Step S2: Obtain the thermal resistance of the transformer Total heat capacity And the heat source, based on the thermal resistance The total heat capacity The average oil temperature of the transformer is derived from the heat source. And based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. Then, adjust the oil temperature at the radiator oil outlet. Temperature is introduced as an open boundary in the coupled computational model; Step S3: Obtain the temperature distribution on the transformer, and determine the temperature value T2 on the coil grid unit of the transformer based on the temperature distribution; Step S4: Based on the absolute value of the difference between the preset temperature value T1 and the temperature value T2, and the preset value... The relationship between the two factors determines whether conductivity needs to be corrected. Step S5: After correcting the conductivity, repeat steps S2, S3 and S4 until the temperature distribution on the transformer shows a convergent state. Obtain the total heat capacity The methods include: According to the equation: It can be concluded that; in, For the quality of the iron core and coil, For the quality of the fuel tank and accessories, The quality of the oil inside the transformer; Alternatively, according to the equation: It can be concluded that; in, This is the fuel tank heat capacity correction factor. For the core heat capacity correction factor, This is the coil heat capacity correction factor. This is a correction factor for the heat capacity of the transformer oil. This is a correction factor for the heat capacity of insulating materials. This refers to the weight of the fuel tank. For the specific heat capacity of the oil tank, For the weight of the iron core, For the specific heat capacity of the iron core, For the weight of the coil, For the specific heat capacity of the coil, This refers to the weight of the oil inside the transformer. The specific heat capacity of the oil inside the transformer. The weight of the insulating material. This refers to the specific heat capacity of the insulating material.

2. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, According to the thermal resistance The total heat capacity The average oil temperature of the transformer is derived from the heat source. The methods include: According to the equation: It can be concluded that; in, The initial average oil temperature over a calculation period. The final average oil temperature over a calculation period. For transformer core losses, This refers to the ohmic losses of the transformer coils. Stray losses within other metal structural components of the transformer; The heat dissipated from the transformer to the air is dissipated; the core loss of the transformer is calculated through simulation based on the transformer's electromagnetic parameters. Ohmic losses in transformer coils And stray losses in other metal structural components of the transformer. .

3. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, The core loss of the transformer is obtained through simulation calculation based on the electromagnetic parameters of the transformer. Ohmic losses in transformer coils And stray losses in other metal structural components of the transformer. The methods include: Step S01: Establish a magnetic field simulation model based on the electromagnetic design parameters of the transformer; Step S02: Input material properties into the magnetic field simulation model; Step S03: Use the current at the minimum voltage tap as the excitation for the magnetic field simulation model.

4. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, The method for calculating the temperature rise of a liquid-immersed transformer also includes: Step S11: Obtain the weight of the transformer's oil tank. Iron core weight Coil weight The weight of the oil inside the transformer Weight of insulation material And use it as input data to obtain the measured value of the transformer's heat capacity and use it as output data; Step S12: Construct a BP neural network and train the BP neural network multiple times to establish a total heat capacity model.

5. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 4, characterized in that, The net input of neurons in the BP neural network and neuron output satisfy: ； ； in, For each input data, This is the heat capacity correction factor. The threshold value is used.

6. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 4, characterized in that, The method for calculating the temperature rise of a liquid-immersed transformer further includes step S110, which is located between step S11 and step S12: The fuel tank weight obtained in step S11 Iron core weight Coil weight The weight of the oil inside the transformer Weight of insulation material The measured values ​​of the transformer's heat capacity were normalized.

7. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, Obtain the thermal resistance of the transformer The methods include: According to the equation: It can be concluded that; in, The heat transfer coefficient is and satisfies: , It is a Nusselt number and satisfies: , For convective heat transfer correlation coefficient, For characteristic length, Thermal conductivity, For heat dissipation area, It is a Grashof number and satisfies: , It is a Prandtl number and satisfies: , For density, For dynamic viscosity, It is the acceleration due to gravity. The rate of change of volume, This refers to the temperature difference.

8. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, Based on the average oil temperature of the transformer The oil temperature at the transformer radiator outlet was obtained. The methods include: According to the equation: It can be concluded that; in, The temperature difference between the inlet and outlet of the transformer radiator must satisfy the following: , This is a correction function for the center height of the coil and the center height of the heat sink.

9. The method for calculating the temperature rise of a liquid-immersed transformer according to claim 1, characterized in that, The method for obtaining the temperature distribution on the transformer includes: The temperature distribution on the transformer is calculated using the physical field analysis of fluid-structure interaction.

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